Method of rolling steel



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United States l atent ()fifice 3,296,846 METHQD @F ROLLING STEEL John It. Guernsey, Crafton Borough, a., assignor to Crucible Steel Company of America, Pittsburgh, Pa, a corporation of New .1 ersey No Drawing. Filed June 5, 1964, Ser. No. 373,075 3 Claims. ((31. 72- 00) This invention relates to a method of rolling certain common austenitic stainless steels and other steels undergoing deformation-induced martensitic transformation during cold rolling.

It is common practice in the stainless-steel industry to produce a hot band of austenitic stainless steel, about 0.100 inch thick, and then cold-roll the hot band to a desired finish thickness, about 0.025 inch. In a typical coldrolling operation, deformation-induced martensitic transformation occurs, making the steel too hard and brittle after 40-60% reduction for further cold rolling without first annealing the steel, a time-consuming and costly operation but for practical purposes an unavoidable one prior to my invention. Aborn U.S. Patent No. 1,918,731 shows that by working at about 200-400 C., deformation-induced transformation is avoided. It has proved impractical, however, to conduct all the needed rolling at such temperature. It is desirable from both operational and quality standpoints to perform finish rolling at or near room temperature.

I have discovered that by conducting an initial portion of the desired total thickness reduction, say about 40% reduction, at an advanced temperature such as 300 B, it becomes possible thereafter to continue to cold-roll at room temperature to the desired thickness without an- In addition to the increase in attainable reduction without annealing, the roll-separating force required for a given thickness reduction is less than for conventional cold rolling, which gives greater reduction per pass and/or less wear and tear on the rolling equipment. If the total desired reduction from hot band to finish gage exceeds about 90%, annealing is probably required, but use of my invention decreases the number of required anneals.

The invention is particularly useful with AlSI Types 201 and 301 steels. The invention does not find use in commercial production of thick pieces requiring only one rolling operation, but is highly advantageous in the production of sheets about 0.060 inch thick or less.

Broadly, the temperature used for the initial warm rolling may be between about 100 F. and the recrystalli- Zation temperature, about 1300 F., preferably between 250 F. and the recrystallization temperature, but for most purposes I prefer to use a temperature of 200 to 400 F. With Type 201 steel, I prefer to use about 300 F., because with a lower temperature. such as 200 F. an intermediate anneal is sometimes required to reduce a hot band to a thickness of about 0.012 inch.

The hot band subjected to my inventive process is about 0.09 to 0.2 inch thick, usually 0.100 to 0.150 inch, or slightly less in narrower widths.

The amount of thickness reduction done at advanced temperature is about 40 to 60%, and the total reduction permissible, warm plus cold, without an intermediate anneal, is up to about 90%. The concept of my invention is distinguished from the practice of the Aborn patent above-mentioned in that substantial further cold rolling is 3,290,846 Patented Jan. 10, 1967 done, so that the total thickness reduction from hot-band gage is about to or more. This makes it possible to produce most of a mills cold-rolled stainless sheets, with thicknesses of 0.018 to 0.060 inch, especially the lighter sheets (0.018 to 0.032 inch), without the norm-ally required intermediate anneal and with the benefits of finish rolling near room temperature. As indicated, however, the invention can be used to yield sheets as thin as 0.005 or 0.002 inch and as thick as 0.080 inch.

The initial warm reduction wholly or partially suppresses the martensitic transformation in subsequent cold rolling, reducing the rate of work hardening. Data are shown below for AISI Type 201, which normally work hardens the most rapidly of the common grades of stainless steel. A minimum initial warm. reduction is necessary to accomplish the desired suppression of martensitic transformation in subsequent working. This has been found to be on the order of 30-40% for AISI Type 201, though some benefit is obtained with lighter initial reductions.

The above-mentioned data for AISI Type 201 steel (carbon 0.15% max., manganese 5.50 to 7.50%, phosphorus 0.060% max., sulfur 0.03% max., silicon 1.00% max., chromium 16.00 to 18.00%, nickel 3.50 to 5.50%, nitrogen 0.25% max, balance iron and impurities) are resented in the following Tables I to III. Table I represents the practice of the invention, and Tables II and III show results with other practices, presented for comparison. Four-inch-diameter rolls were used, and in each case the reported rolling pressures are normalized to the figure required for 10% reduction per pass.

TABLE I.AISI TYPE 201 STEEL ROLLED TO 40% REDUC- TION AT 300 F., FINISHED COLD Total Rolling Reduc- Pressure, Hardness, Thickness, in. tion, Lb. /In. of Re Percent Width TABLE II.AISI TYPE 201 STEEL COLD ROLLED Total Rolling Reduc- Pressure, Hardness, Thickness, m. tio Lb./In. of R Percent Width TABLE III.AISI TYPE 201 STEEL ROLLED TO 80% REDUC- TION AT 300 F.

Table II shows that Type 201 steel work-hardens readily when cold-rolled, requiring high rolling pressures of over 40,000 lb./ in. when cold-reduced to about 40% total reduction or more. Table III shows that by doing all the reduction at 300 F., it is possible to obtain over 80% total reduction with rolling pressures of not over 35,000 lb./in., but as pointed out above, it is undesirable to perform finishing rolling at such a temperature, both because it is operationally inconvenient and because such rolling is detrimental to the quality (surface finish) of the steel. Table I shows that after rolling to 40% total reduction warm (at 300 F.), it is possible to finish the rolling, to over 80% total reduction without requiring high rolling pressures that would necessitate the use of an intermediate annealing operation.

As a specific example, I can produce satisfactory Type 201 stainless-steel sheet as follows. The steel is melted, cast, slabbed, rolled to hot band 0.100 inch thick, annealed, and pickled in the conventional manner. Then, the hot band is heated to about 300 F. and rolled to 40% reduction, i.e., a thickness of 0.060 inch, on a conventional cold rolling mill. The steel is then further rolled on the same or another mill, without additional heating or the necessity of an anneal, to the desired final thickness of 0.025 inch.

While I have shown and described a certain embodiment of the invention, I intend to cover as well any change or modification therein which may be made without departing from the spirit and scope of the invention.

I claim:

1. A method of working deformation-transformable austenitic stainless steel selected from the group consisting of AISI Type 201 and AISI Type 301 stainless steel while suppressing the formation of deformation-induced martensite therein, which consists in Working said steel to effect an initial thickness reduction of about 40 to 60 percent at a temperature between about 100 F. and the recrystallization temperature of said steel and then subsequently further working said steel at about room temperature to effect further thickness reduction such that the total reduction in thickness from said working operations is about 70 to 90 percent.

2. A method of working deformation-transformable austenitic stainless steel selected from the group consisting of AISI Type 201 and AISI Type 301 stainless steel while suppressing the formation of deformation-induced martensite therein, which consists in Working said steel to effect an initial thickness reduction of about 40 to 60 percent at a temperature between about 250 F. and the recrystallization temperature of said steel and then subsequently further working said steel at about room temperature to effect further thickness reduction such that the total reduction in thickness from said working operations is about 70 to 90 percent.

3. A method of working deformation-transformable austenitic stainless steel selected from the group consisting of AISI Type 201 and AISI Type 301 stainless steel while suppressing the formation of deformation-induced martensite therein, which consists in working said steel to effect an initial thickness reduction of about 40 to 60 percent at a temperature between about 250 F. and 400 F. and then subsequently further working said steel at about room temperature to effect further thickness reduction such that the total reduction in thickness from said working operations is about 70 to percent.

4. A method of rolling austenitic stainless steel that develops deformation-induced martensite when coldrolled at about room temperature so that size reduction from a hot-band thickness of about 0.09 to 0.2 inch to a reduced thickness of about 0.015 to 0.080 inch is effected without use of an intermediate anneal, said steel being selected from the group consisting of AISI Type 201 and AISI Type 301 stainless steel, said method comprising first rolling said steel having said hot-band thickness to effect a thickness reduction of about 40 to 60 percent at a temperature of about 200 to 400 F. and then further rolling said steel, without an intermediate anneal, to said reduced thickness at room temperature, the total reduction in thickness from said rolling operations being about 70 to 90 percent.

5. A method of rolling austenitic stainless steel that develops deformation-induced martensite when coldrolled at about room temperature so that size reduction from a hot-band thickness of about 0.100 to 0.150 inch to a reduced thickness of about 0.018 to 0.032 inch is effected withoutuse of an intermediate anneal, said steel being selected from the group consisting of AISI Type 201 and AISI Type 301 stainless steel, said method comprising first rolling said steel having said hot-band thickness to effect a thickness reduction of about 40 to 60 percent at a temperature of about 200 to 400 F. and then further rolling said steel, without an intermediate anneal, to said reduced thickness at room temperature, the total reduction in thickness from said rolling operations being about 70 to 90 percent. 6. A method of rolling austenitic stainless steel that develops deformation-induced martensite when coldrolled at about room temperature so that size reduction from a hot-band thickness of about 0.09 to 0.2 inch to a reduced thickness of about 0.015 to 0.080 inch is effected without use of an intermediate anneal and the lower rollseparating forces are used that are effective to produce a desired, preselected amount of thickness reduction when the steel does not undergo transformation to martensite during rolling, rather than the greater roll-separating forces required to produce said desired, preselected amount of thickness reduction when the steel is undergoing transformation to martensite during rolling, said steel being selected from the group consisting of AISI Type and AISI Type 301 stainless steel, said method comprising first rolling said steel having said hot-band thickness to effect a thickness reduction of about 40 to 60 perclent at a temperature of about 200 to 400 F. and t en further rolling said steel, Without an intermediate anneal, to said reduced thickness at room temperature, the total reduction in thickness from said rolling operations being about 70 to 90 percent.

7. A method of rolling AISI Type 201 austenitic stainless steel so that size reduction from a hot-band thickness of about 0.09 to 0.2 inch to a reduced thickness of about 0.015 to 0.080 inch is effected Without use of an intermediate anneal, said method comprising first rolling said steel having said hot-band thickness to effect a thickness reduction of about 40 to 60 percfint at a temperature of about 200 to 400 F. and t en further rolling said steel, without an intermediate anneal, to said reduced thickness at room temperature, the total reduction in thickness from said rolling operations being about 70 to 90 percent.

8. A method of rolling AISI Type 201 austenitic stainless steel so that size reduction from a hot-band thickness of about 0.09 to 0.2 inch to a reduced thickness of about 0.015 to 0.080 inch is efiected without use of an intermediate anneal and the lower roll-separating forces are used that are eifective to produce a desired, preselected amount of thickness reduction when the steel does not undergo transformation to martensite during rolling, rather than the greater roll-separating forces required to produce said desired, preselected amount of thickness reduction when the steel is undergoing transformation to martensite during rolling, said method comp-rising first rolling said steel having said hot-band thickness to effect a thickness reduction of about to percent at a temperature of about 200 to 400 F. and then further rolling said steel, Without an intermediate anneal, to said reduced thickness at room temperature, the total reduction in thickness from said rolling operations being about to percent.

References Cited by the Examiner UNITED STATES PATENTS 2,606,848 8/1952 Farling et al. 72-202 2,708,379 5/1955 Pakka'la et a1. 72-200 2,934,461 4/1960 Burke et al. 72-202 CHARLES W. LANHAM, Primary Examiner.

H. D. HOINKES, Assistant Examiner. 

1. A METHOD OF WORKING DEFORMATION-TRANSFORMABLE AUSTENITIC STAINLESS STEEL SELECTED FROM THE GROUP CONSISTING OF AISI TYPE 201 AND AISI TYPE 301 STAINLESS STEEL WHILE SUPPRESSING THE FORMATION OF DEFORMATION-INDUCED MARTENSITE THEREIN, WHICH CONSISTS IN WORKING SAID STEEL TO EFFECT AN INITIAL THICKNESS REDUCTION OF ABOUT 40 TO 60 PERCENT AT A TEMPERATURE BETWEEN ABOUT 100*F. AND THE RECRYSTALLIZATION TEMPERATURE OF SAID STEEL AND THEN SUBSEQUENTLY FURTHER WORKING SAID STEEL AT ABOUT ROOM TEMPERATURE TO EFFECT FURTHER THICKNESS REDUCTION SUCH THAT THE TOTAL REDUCTION IN THICKNESS FROM SAID WORKING OPERATIONS IS ABOUT 70 TO 90 PERCENT. 